A scroll compressor has been widely used as a compressor means for compressing gas and increasing the gas pressure. This is because the scroll compressor is superior to reciprocal compressors and rotary compressors in many ways, e.g., low gas leakage, high compressing efficiency, small torque change, low vibration, low noise, etc.
For example, a conventional scroll compressor is constituted as shown in FIG. 1. In FIG. 1, the scroll compressor comprises a sealed case 11, a frame 12, a compressing unit 13 and a driving unit 14. The frame 12 divides the inside of the sealed case 11 into two spaces. The compressing unit 13 is mounted on the frame 12 at the upper space of the sealed case 11. The driving unit 14 is mounted on the frame 12 at the lower space of the sealed case 11. The driving unit 14 has a crank shaft 15 which rotatably penetrates the frame 12.
The compressing unit 13 comprises an orbiting scroll member 16 and a stationary scroll member 17. The orbiting scroll member 16 includes a disc-plate 18 and a spiral wrap 19 formed primarily in an involute curve and attached to one surface of the disc-plate 18 in an upstanding position. The stationary scroll member 17 includes a disc-plate 20 and a spiral wrap 21 formed primarily in an involute curve and attached to one surface of the disc-plate 20 in an upstanding position. The orbiting scroll member 16 and the stationary scroll member 17 are arranged in juxtaposed relation, with the spiral wrap 19 and the spiral wrap 21 thereof being fitted closely together. The orbiting scroll member 16 is moved in orbiting motion by an eccentric shaft portion 22 of the crank shaft 15 while the rotation of the orbiting scroll member 16 on its own axis is inhibited by an Oldham's ring 23 interposed between the orbiting scroll member 16 and the frame 12. The orbiting movement of the orbiting scroll member 16 reduces the compressing space 13a in compressing unit 13 found between the orbiting scroll member 16 and the stationary scroll member 17 and compresses a gas contained therein to increase its pressure.
The disc-plate 20 defines a discharge port 25 at its center O. The upper surface of the disc-plate 20 is covered with a muffler 26. Thus, the gas compressed by both the orbiting scroll member 16 and the stationary scroll member 17 are discharged into a muffler space 26a which is defined by the stationary scroll member 17 and the muffler 26. The muffler space 26a is connected to an outer facility through a discharge pipe 27. One end of the discharge pipe 27 extends into the muffler space 26a through the muffler 26. Another end of the discharge pipe 27 is connected to, e.g., a condenser (not shown) of the outer facility. Thus, the compressed gas is supplied to a condenser in the outer facility.
The gas is then fed back to the scroll compressor from the outer facility through a suction pipe 28. One end of the suction pipe 28 extends into the lower space of the sealed case 11 through the cylindrical wall of the sealed case 11. Another end of the suction pipe 28 is connected to, e.g., an accumulator (not shown) of the outer facility. The fedback gas is sucked in the compressing unit 13 through suction ports (not shown) defined in the disc-plate 18 at its peripheral portion. Thus, the gas is compressed during the orbiting movement of the orbiting scroll member 16.
The scroll compressor further comprises a release port 29 and a release pipe 30. The release port 29 and the release pipe 30 constitute a bypass system together with a control valve (not shown) provided in the outer facility. The release port 29 is defined in the disc-plate 20 at a position offset from the center O by a prescribed distance. One end of the release pipe 30 is coupled to the release port 29. Another end of the release pipe 30 extends outside the scroll compressor by penetrating both the muffler 26 and the sealed case 11 and communicates with the suction pipe 28 through the control valve.
In the scroll compressor, the pressure of the gas in the compressing unit 13 becomes high as the portions of the spiral wrap 19 and the spiral wrap 21 of the orbiting scroll member 16 and the stationary scroll member 17 in contact with each other approach the center O of each the stationary scroll member 17 and the disc-plate 18. This increase in pressure occurs periodically during the orbiting movement of the orbiting scroll member 16. The gas pressure of the supply gas output from the scroll compresser is determined primarily by the rotation speed of the orbiting scroll member 16. Thus, the gas pressure is generally controlled by changing the rotation speed of the orbiting scroll member 16 through the driving unit 14. However, the scroll compressor exhibits its maximum efficiency at a prescribed range of rotation speeds. Thus, the rotation speed should be kept within the range. The bypass system is used for reducing the gas pressure of the supply gas output from the scroll compresser while keeping the rotation speed in the desired range when the demands of the outer facility are lowered.
The conventional scroll compressor is constructed as above, and has some drawbacks, as described below. That is, the release pipe 30 penetrates both the muffler 26 and the sealed case 11, as described above. Further, the release pipe 30 is bent in the muffler space 26a for connecting to the release port 29. In the manufacturing of the actual products, it is very difficult to penetrate both the muffler 26 and the sealed case 11 and then bend the release pipe 30 in the muffler space 26a, or vice versa, without causing leaks. Thus, the conventional scroll compressor as shown in FIG. 1 is not practical for mass production.